US3923467A - Production of ultra fine refractory particles from refractory material using plasma flows and a fluidized bed - Google Patents

Production of ultra fine refractory particles from refractory material using plasma flows and a fluidized bed Download PDF

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Publication number
US3923467A
US3923467A US213052A US21305271A US3923467A US 3923467 A US3923467 A US 3923467A US 213052 A US213052 A US 213052A US 21305271 A US21305271 A US 21305271A US 3923467 A US3923467 A US 3923467A
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enclosure
refractory
flow
particles
plasma
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US213052A
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Claude Bonet
Marc Foex
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Bpifrance Financement SA
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Agence National de Valorisation de la Recherche ANVAR
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/626—Preparing or treating the powders individually or as batches ; preparing or treating macroscopic reinforcing agents for ceramic products, e.g. fibres; mechanical aspects section B
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2/00—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic
    • B01J2/16—Processes or devices for granulating materials, e.g. fertilisers in general; Rendering particulate materials free flowing in general, e.g. making them hydrophobic by suspending the powder material in a gas, e.g. in fluidised beds or as a falling curtain
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J8/00—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes
    • B01J8/18—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles
    • B01J8/24—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique
    • B01J8/42—Chemical or physical processes in general, conducted in the presence of fluids and solid particles; Apparatus for such processes with fluidised particles according to "fluidised-bed" technique with fluidised bed subjected to electric current or to radiations this sub-group includes the fluidised bed subjected to electric or magnetic fields
    • C—CHEMISTRY; METALLURGY
    • C03—GLASS; MINERAL OR SLAG WOOL
    • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
    • C03B19/00—Other methods of shaping glass
    • C03B19/10—Forming beads
    • C03B19/1005—Forming solid beads
    • C03B19/102—Forming solid beads by blowing a gas onto a stream of molten glass or onto particulate materials, e.g. pulverising
    • C03B19/1025—Bead furnaces or burners
    • C03B19/103—Fluidised-bed furnaces
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
    • H05H1/00—Generating plasma; Handling plasma
    • H05H1/24—Generating plasma
    • H05H1/26—Plasma torches
    • H05H1/32—Plasma torches using an arc
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2219/00—Chemical, physical or physico-chemical processes in general; Their relevant apparatus
    • B01J2219/08—Processes employing the direct application of electric or wave energy, or particle radiation; Apparatus therefor
    • B01J2219/0894—Processes carried out in the presence of a plasma

Definitions

  • the device is especially adapted to the partial vaporisation of powdered refractory materials and comprises a vertical enclosure with an exhaust opening to the outside in its upper portion. In its lower portion orientable nozzles provide convergent elementary flows of plasma traversable by an electric current to generate the principal flow of plasma with a flared shape.
  • the cross-section of the principal flow reaches a value equal or close to the internal cross-section of the enclosure.
  • a funnel introduces the powders by gravity into the principal flow.
  • injectors of cold gas into the enclosure above the principal flow and cooling means for the walls can be included.
  • the invention relates to a method and to a device for the thermal treatment, especially with vaporisation of refractory materials and it relates more particularly, because it is in this case that its application seems to have the most advantage, but not exclusively, to a method and a device for the treatment of fairly coarse powders of refractory materials for the purpose of obtaining fine powders of predetermined granulometries for ultra-fine powders.
  • the invention consists to obtain an at least partial vaporisation of powders of refractory materials of a method consisting in making converge into the lower portion of a vertical enclosure, whose walls are, preferably, cooled, elementary flows of plasma traversed by an electric current and emerging from nozzles placed in the proximity to the bottom of the enclosure, in bringing this powder above the convergent point of these elementary flows and of adjusting the angles formed by the directions of the elementary flows, the flow rates of these flows and the electric power dissipated into the latter, so as to form a principal flow flared upwardly andof sufficiently reduced speed to obtain fluidisation of the powder introduced into the principal flow.
  • the invention consists also of a device for the at least partial vaporisation of these powders of refractory materials, comprising an enclosure with vertical axis, whose walls are, preferably, cooled and which have, in its upper portion, an exhaust opening towards the exterior, this device being characterised by the fact that the enclosure comprises, in its lower portion, oriented or orientable nozzles adapted to supply convergent elementary plasma flows and adapted to be traversed by an electric current, these elementary flows giving rise 5 enclosure, and means to introduce the said powders in this principal flow.
  • These installations can be constituted by several plasma torches each being provided with an autonomous supply, one of the electrodes of each of these torches being moreover inserted in a electric circuit, supplied by a common generator and capable of being closed through the elementary flows, as soon as each of the plasma torches of the installation has been ignited.
  • the plasma torches of the above-indicated installation can even be replaced by nozzles devoid of their own electrical supply but each comprising a conductive portion in contact with the corresponding flows, the conductive portions of all these nozzles being inserted in a circuit, normally open, comprising a common device for the supply of electric current and capable of being closed by means of these flows, on the-production in the latter of a sufficient reduction in their electrical resistance.
  • the plasma torches or nozzles concerned are arranged inside or within the walls of the enclosure, in the lower portion of the latter, to obtain above the convergence point of these flows, a principal flow not traversed by an electric current and resulting from the convergence of the elementary flows, this principal flow having, at least at a certain distance from the convergence point of the elementary flows, a crosssection which is close to, or even becomes equal, or tends to become greater then, to the internal cross-sec tion of the enclosure.
  • the invention hence enables the obtaining of a true fluidised bed of the material to be treated, of which the fluidising gas is constituted by the hot gases alone of the principal flow.
  • This fluidised bed has also particular characteristics which show themselves to be of considerable advantage, especially in the case of the preferred application of the invention. Considering, in fact, that the temperature of the hot gases in the flow diminishes from below to above, the average speed of flow of the plasma diminishes equally from below to above.
  • the plasma is a heterogenous medium from the point of view of local temperatures and speeds of flow, does not appear to spoil the efficiency of fluidisation.
  • the ratio of the maximum speeds of fluidisation to the minimum speeds of fluidisation in the principal flow of plasma is sufficiently high for the heterogeneities of temperatures not to cause, in certain zones, movements of the whole of the fluidising bed corresponding either to decantation, or to drawing of the powder under treatment from the bed.
  • Such thermal gradients appear, on the contrary, to favor the movement of particles and their mixing into the principal flow of plasma and, consequently, to improve the quality of heat transfers.
  • This auxiliary current of gas which, if necessary, can be constituted itself by a flow of plasma, can in particular be rendered convergent, with the elementary flows emerging from the aforesaid nozzles.
  • a particularly efficient injection of the particles deposited or which are being deposited in the bottom of the enclosure is obtained if this bottom has a substantially conical or similar surface, the point of the cone being oriented downwardly, the injection of the auxiliary gaseous flow being effected at the level of the point of the cone.
  • auxiliary gaseous current Recourse to this auxiliary gaseous current is of very particular advantage, in the case of effecting discontinuous treatment operations of refractory materials as powder and when the charge to be treated is introduced into the bottom of the enclosure.
  • the auxiliary gaseous current then produces a mixing of this powder and entrains it progressively to the inside of the principal flow where the fluidised bed is created.
  • the gaseous auxiliary current In a particularly advantageous embodiment of the invention and in the case where a continuous thermal treatment is car ried out, recourse will advantageously be had to supply of the enclosure by gravity, the gaseous auxiliary current then serving essentially to re-inject into the fluidised bed the material which has escaped byflow along the walls of the enclosure.
  • the fluidizing plasma will have to be constituted by a gas inert with respect to the refractory material.
  • FIGS. 1 and 2 show diagrammatic cross-sections of embodiments of installations according to the invention for producing vaporisations of refractory materials.
  • FIG. 1 There is shown in diagrammatic manner in FIG. 1 the device which was used in the experimental trial which will be described below, which device comprises an enclosure 2 with cooled walls 4 and comprising, in its upper portion, at least one opening for exhaust 6 towards the outside, this device being more particularly characterised by the fact that it comprises in its lower portion nozzles 8a, 8b, 8c oriented or orientable so as to provide laminar elementary flows 10a, 10b, 10c of a plasmagenic gas converging at a point 12.
  • FIG. 1 the device which was used in the experimental trial which will be described below, which device comprises an enclosure 2 with cooled walls 4 and comprising, in its upper portion, at least one opening for exhaust 6 towards the outside, this device being more particularly characterised by the fact that it comprises in its lower portion nozzles 8a, 8b, 8c oriented or orientable so as to provide laminar elementary flows 10a, 10b, 10c of a plasmagenic gas converging at a point 12.
  • the nozzles concerned are constituted by three plasma torches 14a, 14b, 14c shown in diagrammatic manner, each of these torches comprising its own supply 16 as has been shown in diagrammatic manner for the torch 14a, this autonomous supply enabling the application of a potential differ ence sufficient to support an electric arc between the anodes l8 and the the cathodes 20 of these plasma torches,
  • the anodes 18 of the three plasma torches are inserted in a circuit 22 comprising a three-phase current generator 24, this circuit 22 being adapted to be closed through the elementary flows 10a, 10b, 10c produced by the three plasma torches.
  • the supply of the enclosure can be effected by gravity, as shown in FIG. 1.
  • the powder to be vaporised is introduced by means of a hopper or a funnel 28 placed in the upper portion of the enclosure, the grains of powder being thus brought to fall into the flared portion of the principal flow 26 in which there is then formed a fluidised bed of particles.
  • the particles contained in this hot fluidised bed are vaporised, the vapors and, possibly, the particles, once the latter have undergone a sufficient reduction of volume for the relative maximum fluidisation speeds tobecome less than the speed of flow of the gases of the principal flow, being evacuated through the opening 6 formed in the upper portion of the enclosure.
  • This opening 6 can be connected to a separator.
  • Observation ports 32 enable the checking of the fluidised bed, especially of its movements in the enclosure, which could possibly necessitate correction of the flow rates of the plasmagenic gas of the torches or of the flow rate of the gravity supply to the enclosure of the powder to be treated.
  • auxiliary gaseous current 39 In order to recycle particles 34 which flow along the inner walls 36 of the enclosure and are deposited in the bottom of the latter, recourse is had to an injection of an auxiliary gaseous current 39, by means of a noule shown diagrammatically at 38 in FIG. 1, in the bottom of the enclosure.
  • This auxiliary gaseous current is oriented so as to converge with the elementary flows a, 10b, 10c and its flow rate is adjusted so as to re-entrain the particles being deposited in the bottom of the enclosure, again to the inside of the fluidised bed formed in the principal flow 26.
  • the bottom of the enclosure has the shape of a cone 40 of which the point is oriented downwardly, the injector 38 opening into the inner space of the enclosure, at the point of the cone 40.
  • this injector 38 Apart from this injector 38 enabling continuous recycling of the particles falling into the bottom of the enclosure, it will also be usable as a vehicle for the particles to be treated in the case of effecting discontinuous operations in which, before-the starting of the plasma torches, there has been a prior loading of the bottom of the enclosure with the material to be treated.
  • the flow rate of the injector 38 must be adjusted so as to entrain progressively the whole of the powder to be treated inside the principal flow 26, to form the desired fluidised bed.
  • the discontinuous treatment operation is stopped when a fraction or the whole of the powder initially charged into the enclosure is vaporised.
  • the characteristics of the device were as follows diameter of the enclosure: 250 mm nominal power of each of the three torches 10a, 10b,
  • the nominal power of each of the torches becomes 11.2 kW (560 A at 20 V) when the arcs are started in the elementary flows 10a, 10b, 10c which close the electrical circuit 22 supplied by the triphase current generator 24. The latter then yields a power of 38.5 kW 3 l40V l60A).
  • the fluidisation of the vaporised material is then capable of being started.
  • a processing trial for I00 seconds was carried out on the g of powdered zirconia which had previously been charged into the bottom of the enclosure. At the end of this trial, there were recovered in the bottom of the enclosure 100 g of powder which had not been vaporised, 20 g of powder of extremely fine granulometry on the walls of the enclosure, this powder resulting from the condensation on the cooled walls of the zirconia vaporised in the fluidised bed. Finally, 30 g of zirconia were removed to the outside in the form of vapor and collected outside in the form of extremely fine condensation particles.
  • diameter of the enclosure 250 mm continuous power, supplied by autonomous supplies 16 of each of the torches 14a, 14b, 14c: 12 kW (600 A X 20 V) average maximum power of the three-phase altemating current: 54 kW fix v x A) 7 flow rate of argon of each of the torches 14a, 14b, 14
  • Fraction remaining in the recovery cone The fraction of zirconia vaporised and condensed outside is characterised by granulometries less than 10 microns.
  • the first is constituted by individual grains, of regular shapes, sometimes spherical, having at the surface a system of I very fine nicks,of small dimensions relative to the diameter of the grain.
  • the second is constituted by grains-of very jagged shapes constituted from agglomerates of grains of small diameters, having an arborescent shape, with high specific surfaces. The examination of these grains with a sufficiently powerful optical microscope reveals that the particles of the class 40p. 10p. are in fact constituted by agglomerates of much finer particles, of the order of a micron.
  • FIG. 2 a device more suitable for industrial use than the experimental device which has just been described.
  • the plasma torches 14a, 14b, 14c of the installation in FIG. 1 are advantageously replaced by nozzles of which one has been shown diagrammatically at 54a, these nozzles being devoid of their own electrical supply but'comprising conductive portions in contact with the gaseous flows which they are capable of providing.
  • These nozzles are inserted in a circuit (not shown), normally open, comprising a common electric current supply device, this circuit being closable by means of these flows on the production in the latter of a sufficient reduction in their electrical resistance. It is known that the flow rates of these nozzles of installations of this type are variable to much greater proportions than the flow rates of plasma torches of the preceding assembly.
  • Assemblies such as those described in Pat. No. 1,600,278 or in the application for the certificate of addition No. 46416 already mentioned are usable.
  • the conductive portions of these nozzles are all inserted in a common circuit (not shown) and .respectively connected to the phases of a source of polyphase current (also not shown) comprising a number of phases equal to the number of nozzles provided in the fluidising enclosure.
  • the nozzle cooperates with a pilot plasma torch 56 serving both for the starting and for the maintenance of the electric arcs in the elementary flows 10a, 10b, 10c.
  • the enclosure 2a of the device of FIG. 2 comprises advantageously two stages, namely a first stage 58, in its lower portion, in which the fluidisation proper of the material to be treated under the conditions already described is effected and, in the upper portion of the ap- I 9 paratus, a second stage 60 for tempering the condensation of the vapors escaping from the stage 58.
  • This tempering can be facilitated by the injection of an inert chilling gas into the separating zone 62 of the two stages, by means of injectors 63, these gases, entrained towards the top of the apparatus by the hot gases of the principal-plasma flow, then ensuring both the condensation of the vapors-and their entrainment upwardly and towards a separating device diagrammatically shown at 64 (for example an electrostatic or cyclone separator) where the ultra-fine powders obtained can be collected.
  • a separating device diagrammatically shown at 64 for example an electrostatic or cyclone separator
  • the funnel 28 is closed and communicates with a supply connector 68 for a carrier gas which contributes to the introduction of the powder into the fluidising stage.
  • carrier gas also avoids the risks of clogging of the cooling current end by molten refractory material.
  • the vaporisation yield is very high, and this all the greater as the diameter of the enclosure is greater, considering that the losses of materials and of heat, inevitable on contact with the walls, will be reduced to equivalent proportions;
  • the position of the fluidising bed in the enclosure is adjustable, hence the zone of temperatures in which the fluidising bed is effected, for example, either by adjusting the flow rates of the nozzles, hence the velocity of the flow of the gases in the principal flow, or, when possible, by selecting the granulometries of the starting materials.
  • the minima and maxima velocities of fluidisation of the material in the heart of the principal flow are brought into play.
  • the reactor according to the invention also lends itself well to the treatment of powders whose granulometries vary over wide ranges, the reactor then being of integral type.
  • the invention is capable of numerous applications. other than simple vaporisation in the heart of an inert gaseous flow of refractory materials which has been more particularly envisaged in the foregoing.
  • zirconium silicate or zircon which decomposes into silica, into zirconia and into impurities; in this particular case the later separation of the various constituents is easily realisable mechanically, for the production of deposits from a vapor phase, for chemistry at high temperatures, which brings into play heterogeneous reactions between the fluidised solid phase and the hot gaseous phase provided by the flows, etc.
  • a method for the production of ultra fine refractory particles from a refractory material in the fonn of relatively coarse particles which comprises generating a plurality of upwardly directed plasma flows in the lower portion of a vertical enclosure, the direction of said plasma flows being oriented to converge at a point substantially at the vertical axis of said enclosure to form a principal flow of hot gases moving upwards, said gases having a temperature above the vaporization temperature of said refractory particles, causing an electric current to flow through said convergent flows in an arc across the bottom of the enclosure at an energy level of at least about 38.5 kw, introducing said refractory coarse particles by gravity into said principal flow of hot gases above said point of convergence, controlling the orientations and the flow rates of said plasma flows and the electrical energy dissipated therein to impart to said principal flow a flared shape terminating in a cross-section substantially equal to the internal diameter of said enclosure, said plasma flows having a sufficiently reduced speed so as to form a fluidized bed of said refractory particles there
  • auxiliary gaseous current is itself constituted by a plasma 4.
  • an auxiliary gaseous current is injected into the enclosure, at its bottom, at a flow rate adapted to entrain into the principal flow particles present in the bottom of the enclosure.
  • a method for the production of ultra fine refractory particles from a refractory material in the fonn of relatively coarse particles which comprises generating a plurality of upwardly directed plasma flows in the gases above said point of convergence, controlling the lower portion of a vertical enclosure, the direction of form a principal flow of hot gases moving upwards, said,

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Organic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Materials Engineering (AREA)
  • Ceramic Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Structural Engineering (AREA)
  • Combustion & Propulsion (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
  • Devices And Processes Conducted In The Presence Of Fluids And Solid Particles (AREA)
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US213052A 1971-01-06 1971-12-28 Production of ultra fine refractory particles from refractory material using plasma flows and a fluidized bed Expired - Lifetime US3923467A (en)

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FR7100184A FR2120491A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1971-01-06 1971-01-06

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US (1) US3923467A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
BE (1) BE777762A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
CH (1) CH562055A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
DE (1) DE2200448A1 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
FR (1) FR2120491A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)
GB (1) GB1381606A (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4013415A (en) * 1974-06-07 1977-03-22 Igor Sergeevich Burov Plasma-chemical reactor for treatment of disperse materials
US4174203A (en) * 1976-05-05 1979-11-13 Swiss Aluminium Ltd. Process and device for the production of submicron-sized metallic oxides
US4941965A (en) * 1987-05-22 1990-07-17 Electricite De France (Service National) Process for the hydrocracking of a hydrocarbon feedstock and hydrocracking plant for carrying
US20030141820A1 (en) * 2002-01-30 2003-07-31 Applied Materials, Inc. Method and apparatus for substrate processing

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3429665A (en) * 1964-05-13 1969-02-25 British Titan Products Production of pigmentary size titanium dioxide
US3431074A (en) * 1966-11-15 1969-03-04 Cabot Corp Process for the production of highly amorphous carbon black
US3524496A (en) * 1966-12-08 1970-08-18 William Richard Barnes Fine particles
US3532462A (en) * 1963-04-27 1970-10-06 Bayer Ag Method of effecting gas-phase reactions
US3596040A (en) * 1967-07-11 1971-07-27 British Titan Products Heating particulate material

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3532462A (en) * 1963-04-27 1970-10-06 Bayer Ag Method of effecting gas-phase reactions
US3429665A (en) * 1964-05-13 1969-02-25 British Titan Products Production of pigmentary size titanium dioxide
US3431074A (en) * 1966-11-15 1969-03-04 Cabot Corp Process for the production of highly amorphous carbon black
US3524496A (en) * 1966-12-08 1970-08-18 William Richard Barnes Fine particles
US3596040A (en) * 1967-07-11 1971-07-27 British Titan Products Heating particulate material

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4013415A (en) * 1974-06-07 1977-03-22 Igor Sergeevich Burov Plasma-chemical reactor for treatment of disperse materials
US4174203A (en) * 1976-05-05 1979-11-13 Swiss Aluminium Ltd. Process and device for the production of submicron-sized metallic oxides
US4941965A (en) * 1987-05-22 1990-07-17 Electricite De France (Service National) Process for the hydrocracking of a hydrocarbon feedstock and hydrocracking plant for carrying
US20030141820A1 (en) * 2002-01-30 2003-07-31 Applied Materials, Inc. Method and apparatus for substrate processing
WO2003063947A3 (en) * 2002-01-30 2004-04-08 Applied Materials Inc Method and apparatus for substrate processing

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CH562055A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1975-05-30
FR2120491A5 (GUID-C5D7CC26-194C-43D0-91A1-9AE8C70A9BFF.html) 1972-08-18
DE2200448A1 (de) 1972-07-20
BE777762A (fr) 1972-07-06
GB1381606A (en) 1975-01-22

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